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Recorded bird calls entice warblers to nest in conservation areas

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CHAMPAIGN, Ill., 10/9/17: Some species of migrating songbirds return each year to their favorite summer home in the Midwest, where food and nesting sites are plentiful. A University of Illinois scientist and a biologist from the Wisconsin Department of Natural Resources found that recorded birdsongs could coax endangered Kirtland’s warblers to a new breeding site hundreds of miles from their usual destination for their own protection.

In 2016, the last year of the three-year study, the researchers attracted a population of Kirtland’s warblers to a Wisconsin forest using Mp3 players to transmit birdsongs, even though these birds tend to flock to Michigan’s Lower Peninsula to nest.

“This behavioral trick has been used in various studies over short distances, but this is the first research project to successfully demonstrate the potential to expand migratory bird geographic range over much greater distances,” said Mike Ward, scientist with the Illinois Natural History Survey, a division of the Prairie Research Institute. “If we can influence where species decide to breed, we can put rare and endangered bird species in forests where we have the resources to conserve and protect them.”

As bird habitats change and shrink because of climate change, urban development, and agricultural practices, conservationists need new tools to manage threatened and endangered flocks. Relocation reduces the risk of a catastrophic event that could wipe out a population or a species, establishes a population on public land where management is easier, and provides the birds with potentially higher-quality habitat.

In 2013, the research team selected a Wisconsin location on public land with the most suitable forest stands. Male Kirtland’s warblers had been seen in the area previously, but not that year, and warblers had not bred in the area. The team played male warbler birdsongs from May 2 to July 31 in 2014–2016, signaling to migrating birds that a male warbler had selected a territory and that habitat was available.

Researchers broadcast the distinctive and loud Kirtland’s warbler song both at night and during the day. Like most other migratory birds, Kirtland’s warblers migrate at night but sing more frequently in the early morning hours. The goal of playing the songs was to both attract birds to the site and then entice the birds to stay.

“Using calls at night when birds migrate helps to bring male and female warblers to the same place at the same time,” Ward said. “If no other warblers were there, they would likely leave quickly in search of another location, much like if you went to a restaurant and no one else was there, you would likely leave thinking something was wrong with that restaurant.”

With no recorded birdsong in a forest plot, male warblers would either fly by or stop briefly, then fly away. Ward supposed that Kirtland’s warblers might not have populated the site for years or even decades.

Relocation will only be successful, however, if managers fully understand species-specific bird behavior. Broadcasting birdsong to lure other bird species to new areas might work, but it could be “a risky proposition,” Ward said.

“You wouldn’t want to move an endangered species to a location where they wouldn’t breed,” he said.

This study was published in the journal Diversity and Distributions (DOI: 10.1111/ddi.12635), and was funded by the U.S. Army Construction Engineering Research Laboratory.